Method for vacuum impulse forming of heated glass sheets

ABSTRACT

Apparatus (20,120) for forming a heated glass sheet G is disclosed as including a vacuum mold (22,22a,122,122a) having a full surface (24,24a,124,124a) against which a peripheral mold (26,26a,126,126a) presses the glass sheet periphery and with which at least one vacuum reservoir (32,33) is communicated within the interior of the sealed glass sheet periphery to form the glass sheet to the shape of the vacuum mold surface. Valving (38) of a vacuum system (28) is preferably operable to provide the vacuum impulse in two stages with an initial limited extent of vacuum and a subsequent greater extent of vacuum by communication first with one vacuum reservoir (32) and subsequently with another vacuum reservoir (33). Different embodiments of the vacuum mold have the vacuum mold surface facing upwardly and downwardly with convex and concave shapes. Glass sheet shapes including straight line elements such as cylindrical and conical bends as well as shapes including curvatures in transverse directions and inverse curvatures can be effectively provided by this vacuum impulse forming.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a 371 of PCT/US91/02142, filed Mar. 28, 1991, which is acontinuation of U.S. patent application Ser. No. 07/527,116, filed May22, 1990, now abandoned.

TECHNICAL FIELD

This invention relates to vacuum forming of heated glass sheets.

BACKGROUND ART

Vacuum forming of heated glass sheets against a curved mold surface hasbeen performed for many years. Such vacuum forming is usually performedby drawing a vacuum within openings in the mold surface. The extent ofvacuum utilized is normally on the order of about several to 10 inches(about 10 to 25 cm.) water column. Such a conventional vacuum can beprovided by commercially available hot operating fans that arepositioned within a heated environment in which the vacuum forming isperformed and can also be provided by a gas jet pump such as disclosedby U.S. Pat. No. 4,222,763 McMaster wherein a primary gas flow isintroduced into a passageway through jet openings which have axial andcircumferential components that are substantially tangent to the innersurface of the passageway such that the primary gas flow induces asecondary gas flow that generates the vacuum through suitablecommunication passageways.

Prior art glass sheet vacuum forming systems are disclosed by U.S. Pat.No. 3,778,244 Nedelec et al; U.S. Pat. No. 4,661,141 Nitschke et al;U.S. Pat. No. 4,711,653 Frank et al; U.S. Pat. No. 4,746,348 Frank etal; and U.S. Pat. No. 4,859,225 Kuster et al.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a method for providingimproved vacuum forming of heated glass sheets by the use of a vacuumimpulse which involves a substantially greater vacuum than has beenheretofore utilized in vacuum forming of glass sheets.

In carrying out the above object and other objects of the invention,apparatus for forming a heated glass sheet includes a vacuum mold havinga full surface that defines a shape to which the glass sheet is to beformed and also includes a peripheral mold for forming and sealing theperiphery of the glass sheet against the surface of the vacuum mold. Aconduit provides a preferred means for communicating the vacuum moldsurface within the sealed periphery of the glass sheet with at least onevacuum reservoir to provide a vacuum impulse that forms the glass sheetto the shape of the vacuum mold surface.

Since the hot glass sheet has viscoelastic characteristics, the greatervacuum for a shorter time, as compared to conventional forming of glasssheets by vacuum, reduces optical distortion resulting from the glasssurface engagement with the mold surface. More specifically, the vacuumdrawn at the vacuum mold surface within the sealed periphery of theglass sheet is large enough to fully form the glass sheet to the shapeof the mold surface but is not applied long enough to overcome the largeviscous characteristics of the glass such that reduced opticaldistortion results at the interface of the glass sheet and the mold.

The conduit that provides the preferred means for communicating betweenthe vacuum mold and each vacuum reservoir preferably includes valvingthat controls the communication in applying the vacuum impulse. Thisvalving includes at least one valve for: (a) closing the conduit toisolate the vacuum mold from each vacuum reservoir; (b) initiallyopening the conduit to commence the vacuum impulse at a first level ofvacuum; and (c) finally opening the conduit to provide the vacuumimpulse to the vacuum mold at a second greater level of vacuum. A pairof vacuum reservoirs of the apparatus provide the initial vacuum impulseat the first level of vacuum and the subsequent vacuum impulse at thesecond greater level of vacuum. A vacuum pump of the apparatus draws avacuum within each vacuum reservoir.

Different embodiments of the apparatus are disclosed with the vacuummold having its full surface facing both upwardly and downwardly andhaving both convex and concave shapes.

One of the embodiments of the apparatus with the upwardly facing vacuummold surface has this mold surface provided with a convex shape and hasits peripheral mold facing downwardly with a concave shape. Anotherembodiment of the apparatus with the upwardly facing vacuum mold surfacehas this mold surface provided with a concave shape and has itsperipheral mold facing downwardly with a convex shape. The embodimentsof the apparatus with the upwardly facing mold surface each include anactuator that moves the peripheral mold downwardly to press theperiphery of the glass sheet against the upwardly facing vacuum moldsurface.

One of the embodiments of the apparatus with the downwardly facingvacuum mold surface has this mold surface provided with a concave shapeand has its peripheral mold facing upwardly with a convex shape. Anotherembodiment of the apparatus with the downwardly facing vacuum moldsurface has this mold surface provided with a convex shape and has itsperipheral mold facing upwardly with a concave shape. The embodiments ofthe apparatus with the downwardly facing vacuum surface each include anactuator that moves the vacuum mold downwardly such that the upwardlyfacing peripheral mold presses the periphery of the glass sheet againstthe downwardly facing vacuum mold surface.

Both the upwardly and downwardly facing embodiments of the vacuum moldsurface are disclosed as having versions with straight line elementsover the entire extent thereof, curved shapes in directions that aretransverse to each other, and inversely curved portions.

The peripheral mold that presses the periphery of the glass sheetagainst the vacuum mold surface is preferably constructed as a ring moldwith an open center.

In carrying out the above mentioned object and other objects of theinvention, the method for forming a heated glass sheet in accordancewith the invention includes sealing the periphery of the glass sheetagainst a full surface vacuum mold and communicating the vacuum moldsurface within the sealed periphery of the glass sheet with at least onevacuum reservoir to provide a vacuum impulse of at least 0.1 atmospheresof vacuum to elastically form the glass sheet to the shape of the vacuummold surface, and the vacuum impulse is thereafter terminated at apredetermined time so as to reduce optical distortion of the hot glasssheet as a result of engagenent with the mold surface.

In performing the method, the vacuum impulse is preferably provided atthe vacuum mold surface initially at a first level of vacuum andthereafter at a second greater level of vacuum. The first and secondlevels of vacuum are disclosed as being provided by communicating thevacuum mold surface with a pair of vacuum reservoirs. Two differentversions are disclosed for performing the method. In one version, theglass sheet periphery is sealed against the vacuum mold surface by apressing operation of a peripheral mold which maintains the pressingrelationship as the vacuum impulse is provided at the vacuum moldsurface to form the glass sheet. In another version, the glass sheetperiphery is initially sealed against the vacuum mold surface by apressing operation of a peripheral mold which is thereafter positionedout of engagement with the glass sheet as the vacuum impulse is providedat the vacuum mold surface to form the glass sheet.

The objects, features and advantages of the present invention arereadily apparent from the following detailed description of the bestmodes for carrying out the invention when taken in connection with theaccompanied drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partially sectioned view of one embodiment of apparatusconstructed in accordance with the present invention to perform themethod thereof for vacuum forming of a heated glass sheet with a lowervacuum mold having an upwardly facing convex shape and with an upperperipheral mold having a downwardly facing concave shape;

FIG. 2 is a plan view of the apparatus taken along the direction of line2--2 in FIG. 1 to illustrate both the upwardly facing vacuum moldsurface against which the vacuum forming is performed and the downwardlyfacing peripheral mold shape that initially seals the glass sheetperiphery with the vacuum mold surface;

FIG. 3 is a view that illustrates the apparatus of FIGS. 1 and 2 at thecommencement of the vacuum forming cycle;

FIG. 4 illustrates the apparatus of FIGS. 1 and 2 at a further stage ofthe vacuum forming cycle where the peripheral mold has been moveddownwardly to seal the glass sheet periphery against the vacuum moldsurface;

FIG. 5a is a sectional view taken along the direction of 5a--5a of FIG.4 to illustrate the manner in which more simple shapes can be vacuumformed with the peripheral mold maintaining a pressing relationship withthe glass sheet periphery as a vacuum impulse is provided to form theglass sheet;

FIG. 5b is a view taken in the same direction as FIG. 5a and illustratesthe vacuum mold with its surface shaped so as to provide cross-curvaturetransverse to the curvature illustrated in FIG. 4 as well asillustrating a spaced relationship of the peripheral mold to the glasssheet when formed by the vacuum impulse against the vacuum mold surfacewith this more complex shape;

FIG. 5c is a view of the apparatus also taken in the same direction asFIG. 5a and having its vacuum mold surface constructed so as to provideinverse curves as well as illustrating the peripheral mold spaced fromthe glass sheet as in FIG. 5b when the vacuum forming is performedagainst the vacuum mold surface with this more complex inversely curvedshape;

FIG. 6 is a view taken in the same direction as FIG. 4 and illustratesthe formed glass sheet transferred from the lower vacuum mold to theupper peripheral mold in connection with subsequent delivery forcooling;

FIG. 7 is a view of another embodiment of the apparatus for vacuumforming a heated glass sheet wherein an upper vacuum mold has adownwardly facing concave surface against which a lower peripheral moldof an upwardly convex shape presses the glass sheet;

FIG. 8 is a plan view taken along the direction of line 8--8 in FIG. 7to illustrate both the downwardly facing upper vacuum mold surface andthe lower peripheral mold shape that presses the glass sheet against theupper vacuum mold surface;

FIG. 9 is a view of the apparatus of FIGS. 7 and 8 illustrated at thecommencement of the vacuum forming cycle with the heated glass sheetsupported by the lower peripheral mold;

FIG. 10 is a view of the apparatus of FIGS. 7 and 8 at a further stageof the cycle where the heated glass sheet has its periphery pressedagainst the vacuum mold surface;

FIG. 11a is a sectional view of the apparatus taken along the directionof line 11a--11a in FIG. 10 and illustrates the manner in whichstraight-line element shapes are formed with the vacuum mold andperipheral mold maintained in a pressing relationship with the glasssheet periphery;

FIG. 11b is a sectional view taken in the same direction as FIG. 11a andillustrates the apparatus with its vacuum mold surface shaped so as toprovide cross-curvature to the curvature shown in FIG. 10 and alsoillustrates the manner in which the peripheral mold is moved out ofengagement with the glass sheet as the vacuum is provided to form such amore complex shape;

FIG. 11c is also a view taken in the same direction as FIG. 11a with thevacuum mold surface having inverse curves in a direction transverse tothe curvature shown in FIG. 10 and likewise illustrates the peripheralmold in a spaced relationship from the glass sheet during the vacuumforming to this more complex shape;

FIG. 12 illustrates the apparatus at a further stage with the moldsmoved into a farther spaced relationship in preparation for delivery ofthe formed glass sheet from the upper vacuum mold for cooling;

FIG. 13 is a view of another embodiment of the apparatus for vacuumforming a heated glass sheet wherein a lower vacuum mold has an upwardlyfacing concave surface against which an upper peripheral mold of adownwardly convex shape presses the glass sheet:

FIG. 14 is a plan view of the apparatus taken along the direction ofline 14--14 in FIG. 13 to illustrate both the upwardly facing vacuummold surface against which the vacuum forming is performed and thedownwardly facing peripheral mold shape that initially seals the glasssheet periphery with the vacuum mold surface;

FIG. 15 is a view of another embodiment of the apparatus for vacuumforming a heated glass sheet wherein a lower vacuum mold has adownwardly facing vacuum mold surface of a downwardly facing convexshape against which a lower peripheral mold of an upwardly concave shapepresses the periphery of the glass sheet; and

FIG. 16 is a plan view of the apparatus taken along the direction ofline 16--16 in FIG. 15 to illustrate both the downwardly facing vacuummold surface against which the vacuum forming is performed and theupwardly facing peripheral mold shade that initially seals the glasssheet periphery with the vacuum mold surface.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to FIG. 1 of the drawings, one embodiment of apparatus 20for forming a heated glass sheet G in accordance with the presentinvention includes a vacuum mold 22 having a full surface 24 thatdefines a shape to which the glass sheet is to be formed. A peripheralmold 26 of the apparatus provides forming and sealing of the peripheryof the glass sheet against the surface 24 of the vacuum mold 22 as ishereinafter more fully described. A vacuum system 28 of the apparatushas a conduit 30 that provides a preferred means for communicating thevacuum mold surface 24 within the sealed periphery of the glass sheetwith at least one vacuum reservoir 32, and preferably also with a secondvacuum reservoir 33, to provide a vacuum impulse of at least 0.1atmospheres of vacuum to elastically form the glass sheet to the shapeof the vacuum mold. This vacuum impulse provides a much greater extentof vacuum than with conventional glass sheet vacuum forming but only fora limited time to reduce optical distortion of the viscoelastic hotglass sheet as a result of its engagement with the vacuum mold surface24.

With combined reference to FIGS. 1 and 2, the vacuum mold 22 has avacuum chamber 34 to which the conduit 30 is communicated, and thevacuum surface 24 has a set of openings 36 that extend to the vacuumchamber such that the vacuum impulse from the vacuum reservoir 32 isapplied through these openings to the glass sheet to provide the formingto the shape of the vacuum mold surface. These openings 36 in the vacuummold surface 24 are preferably arranged as shown in FIG. 2 just inside,i.e. about 2-4 inches (about 5 to 10 cm.), the location at which theperipheral mold 26 provides the sealing of the glass sheet peripheryagainst the vacuum mold surface.

The vacuum system 28 of the apparatus as illustrated in FIG. 1, inaddition to including the conduit 30 that extends between the vacuummold 22 and each vacuum reservoir 32 and 33, also includes valving 38that controls communication of the vacuum mold and the vacuum reservoirthrough the conduit. This valving 38 is disclosed as including a flowcontrol valve 39 and an on-off valve 40 along a conduit branch 41 thatcommunicates the conduit 30 with the one vacuum reservoir 32. Valving 38also includes a flow control valve 42 and an on-off valve 43 along aconduit branch 44 that communicates the conduit 30 with the secondvacuum reservoir 33. Another on-off valve 46 along a conduit branch 47controls the supply of pressurized gas from a source 45 to the conduit30 for delivery to the vacuum mold 22. As is hereinafter more fullydescribed, the valving 38 initially closes the conduit 30 so as to beisolated from each of the vacuum reservoirs 32 and 33 as well as fromthe pressurized gas source 45. As is hereinafter more fully described,the valving 38 through the flow control valve 39 and the on-off valve 40initially opens the conduit branch 41 to communicate the one vacuumreservoir 32 with the vacuum mold 34 to initially provide the vacuumimpulse at a first level of vacuum. Thereafter upon closing of the valve40 to isolate the one vacuum reservoir 32 from the vacuum mold 22, thevalves 42 and 43 communicate the branch conduit 44 with the secondvacuum reservoir 33 to provide a vacuum impulse to the vacuum mold 22 ata second greater level of vacuum. The vacuum within the pair of vacuumreservoirs 32 and 33 is provided by a vacuum pump 48 through a branchedconduit 49 whose branches have associated regulator valves 50 and 51.

The extent of the vacuum impulse provided at the vacuum mold 22 must begreat enough to elastically deform the glass sheet as it initially isformed to the shape of the mold surface. Thereafter, viscous flow of theglass maintains the glass sheet in its formed shape. The extent ofvacuum necessary to do this elastic forming is controlled by variableswhich include: the size of the vacuum mold chamber 34, the extent of anyleakage which occurs around the periphery of the sealed glass sheet, thesize of each vacuum reservoir 32 and 33, and the extent of the vacuumdrawn within each vacuum reservoir 32 and 33 by the vacuum pump 48.Satisfactory results have been achieved by applying an initial vacuum ofabout 0.1 to 0.3 atmospheres of vacuum for about 0.5 to 2 seconds and bythereafter applying a second greater vacuum of about 0.25 to 0.7atmospheres of vacuum for about 0.5 to 6 seconds. The regulator valves50 and 51 function to communicate the continuously running vacuum pump48 with the associated vacuum reservoirs 32 and 33 so as to maintain avacuum within these reservoirs on the order of about 1/6 to 2/3 of anatmosphere of vacuum. Along each conduit branch 41 and 44, theassociated flow control valves 39 and 42 control the flow area whichcontrols the rate at which the vacuum impulse is applied and therebyprevents excessively fast forming that can cause breakage when the glasssheet hits the mold surface.

As illustrated in FIG. 3, the cycle of glass sheet forming begins withthe glass sheet G deposited on the upwardly facing mold surface 24 ofthe lower vacuum mold 22. It is possible to initially deposit the glasssheet G onto the lower vacuum mold 22 in different ways. For example,the vacuum mold 22 may have a connection 52 to a suitable actuator thatmoves the vacuum mold horizontally to below a suitable topside transferdevice that supports and subsequently releases the glass sheet onto thevacuum mold prior to subsequent movement of the vacuum mold back belowthe peripheral mold 26 as illustrated in FIG. 3. The vacuum conduit 30has a suitable separable coupling or is flexible to permit suchmovement. It is also possible for the topside transfer device to bemoved horizontally to a position above the vacuum mold 22 and to thenrelease the glass sheet onto the vacuum mold with the upper peripheralmold 26 raised as illustrated in FIG. 3.

The apparatus 20 illustrated in FIG. 1 has the surface 24 of its vacuummold 22 facing upwardly with a concave shape and the vacuum mold thusoccupies a lower position with respect to the peripheral mold 26 whichoccupies an upper position. This upper peripheral mold 26 facesdownwardly with a concave shape complementary to the convex shape of thevacuum mold surface 24. Another embodiment of the glass sheet formingapparatus illustrated in FIGS. 13 and 14 is similar to the embodiment ofFIGS. 1 and 2 and thus has like reference numerals with the subscript"a" applied to like components thereof and most of the prior descriptionis applicable except as will be noted. However, the lower vacuum moldsurface mold 24a of the apparatus 22a has an upwardly facing concaveshape and the downwardly facing peripheral mold 26a has a convex shapecomplementary to the upwardly facing concave vacuum mold surface 24a.This upwardly facing concave vacuum mold surface 24a as shown in FIG. 14has its openings 36a located adjacent the peripheral mold as with theembodiment shown in FIG. 2. The vacuum system 28 shown in FIG. 13utilized with the forming apparatus 20a is the same as the vacuum systemutilized with the embodiment shown in FIG. 1.

An actuator 54 of the apparatus 22 shown in FIG. 1 has a connection 56to the upper peripheral mold 26 and is operable to move the peripheralmold vertically with respect to the lower vacuum mold 22 in order toprovide relative movement between the two molds. More specifically, theactuator 54 through its connection 56 moves the upper peripheral mold 26downwardly from the position of FIG. 3 to the position of FIG. 4 suchthat its concave shape presses the periphery of the glass sheet Gagainst the upwardly facing convex surface 24 of the lower vacuum mold22 in preparation for the vacuum impulse forming as previously describedin connection with the vacuum system 28. Likewise with the embodiment ofFIG. 13, the actuator 54a through its connection 56a moves the upperperipheral mold 26a downwardly such that its convex shape presses theperiphery of the glass sheet G against the upwardly facing concavesurface 24a of the lower vacuum mold 22a in preparation for the vacuumimpulse forming as previously described in connection with the vacuumsystem 28.

In performing the vacuum forming, the vacuum mold surface 24 can havedifferent configurations such as illustrated by FIGS. 5a, 5b and 5c.More specifically, as illustrated in FIG. 5a, the vacuum mold surface24a has straight line elements over its entire extent such as is thecase with cylindrical and conical shapes where a straight line can bedrawn through every point on the surface. With such surfaces, the glasssheet forming can be performed with the peripheral mold 26 maintained inpressing engagement with the glass sheet periphery as illustrated. Asillustrated in FIG. 5b, the vacuum mold surface 24b has cross-curvaturein a direction transverse to the curvature illustrated in FIG. 4 and,with such more complex shapes, the upper peripheral mold 26 ispreferably moved into a spaced relationship out of engagement with theglass sheet periphery so as to permit the glass sheet to move along thevacuum mold surface during the vacuum impulse forming. Likewise, asillustrated in FIG. 5c, the vacuum mold surface 24c has inversely curvedportions 58 and 60 in a direction transverse to the curvatureillustrated in FIG. 4. These inversely curved portions 58 and 60 havecenters of curvature on the opposite sides of the mold surface andforming of this more complex Shape, like the cross-curvature indicatedin FIG. 5b, is preferably performed with the upper peripheral mold 26spaced from the glass sheet periphery. The vacuum mold surface 24a ofthe FIG. 13 embodiment of the forming apparatus likewise can havestraight line elements over its entire extent, curved shapes indirections that are transverse to each other, and inversely curvedportions.

As best illustrated in FIG. 3, the peripheral mold 26 preferably is aring 62 having an open center 63 such that the upper glass sheet surfaceis only engaged at its periphery during the forming. An enclosure 64 ofthe peripheral mold as best illustrated in FIG. 6 defines a vacuumchamber 66 in which a vacuum is drawn by a gas jet pump or fan 68mounted on top of the enclosure or at another remote location. After thevacuum impulse forming of the glass sheet is completed, the vacuum mold22 releases the formed glass sheet from its surface 24, preferably withan assist from the pressurized gas source 45 previously described inconnection with FIG. 1, and the formed glass sheet is then received andsupported by the vacuum drawn within the upper peripheral mold 26 whichis then moved upwardly to the position of FIG. 6 in preparation forsubsequent delivery of the formed glass sheet for cooling. A shaperetention pad 70 is helpful with many glass shapes and is mounted byadjustable supports 72 within the open mold ring center 63 as shown inFIG. 2. This shape retention pad 70 prevents the vacuum drawn within theperipheral mold vacuum chamber 66 shown in FIG. 6 from forming the glasssheet excessively upwardly to a concave shape within the center of theperipheral mold 26. Thereafter, the formed glass is delivered from theperipheral mold 26 for cooling such as by delivery to an annealing ringfor slow cooling that provides an annealed glass sheet or to a quenchring for quenching that provides a tempered glass sheet. It should benoted that the apparatus 20a is illustrated in FIG. 13 with itsdownwardly convex upper peripheral mold 26a lacking any shape retentionpad like the shape retention pad 70 illustrated with the concaveembodiment of FIG. 1; however, it should be appreciated that the shaperetention pad could also be used with the FIG. 13 embodiment.

With reference to FIG. 7, another embodiment of the apparatus isidentified by 120 and includes a vacuum mold 122 that occupies an upperposition such that its full surface 124 faces downwardly. Thisdownwardly facing vacuum mold surface 124 has a downwardly concaveshape. The peripheral mold 126 of this embodiment occupies a lowerposition with its curved shape facing upwardly with a convexconfiguration that is complementary to the downwardly facing concavesurface 124 of the upper vacuum mold 122. The vacuum system 28communicates the upper vacuum mold 122 with the vacuum reservoir 32 bycommunication with its chamber 134 which is communicated by openings 136with the vacuum mold surface 124. These openings 136 as shown in FIG. 8are preferably located just inwardly from the location at which thelower peripheral mold 126 presses the glass sheet periphery against themold surface 124 during the forming cycle.

As illustrated in FIG. 9, the glass sheet forming cycle begins with theglass sheet initially deposited on the lower peripheral mold 126 with anactuator 154 through its connection 156 to the upper vacuum mold 122providing positioning of the molds in a spaced relationship to eachother. The lower peripheral mold 126 may be moved horizontally by anactuator connection 152 to receive the heated glass sheet from a topsidetransfer device or the topside transfer device may be moved horizontallyover the lower peripheral mold to deposit the glass sheet thereon forforming. Thereafter, the actuator 154 moves the vacuum mold 122downwardly such that the peripheral mold 126 presses the periphery ofthe glass sheet against the downwardly facing surface 124 of the vacuummold. The vacuum conduit 30 is flexible to permit the vertical movementof the vacuum mold 122.

As illustrated in FIGS. 11a, 11b and 11c, the cycle proceeds to provideglass sheet forming to a configuration that depends upon the ultimateformed shape desired. More specifically, the glass sheet G as shown inFIG. 11a is pressed against a surface 124a with straight line elementssuch as is the case with cylindrical or conical bends and, in suchcases, the peripheral mold 126 is maintained in pressing engagement withthe glass sheet periphery. It is also possible to providecross-curvature such as indicated by the vacuum mold surface 124b inFIG. 11b with such curvature being transverse to the curvatureillustrated in FIG. 10 and, in such cases, the lower peripheral mold 126is moved into a spaced relationship with the glass sheet periphery topermit such more complex shaped forming to proceed. Likewise asillustrated in FIG. 11c, the vacuum mold surface 124c may have inverselycurved portions 158 and 160 in a direction transverse to the curvatureillustrated in FIG. 10 and the lower peripheral mold 126 will then alsobe maintained in a spaced relationship to the glass sheet peripheryduring the vacuum forming.

The glass sheet is then formed on the downwardly facing vacuum moldsurface 124 by the vacuum impulse of the vacuum system 28 with the twostage vacuum previously described in connection with the embodiment ofFIGS. 1 through 6. The formed glass sheet is ultimately delivered by theupper vacuum mold 122 for cooling such as on an annealing ring toprovide an annealed glass sheet or on a quench ring for quenching thatprovides a tempered glass sheet. The pressurized gas supplied from thegas source 44 of the vacuum system 28 provides a release of the glasssheet from the downwardly facing surface 124 upper vacuum mold 122 uponsuch delivery.

With reference to FIGS. 15 and 16, another embodiment of the formingapparatus 120a is similar to the embodiment of FIGS. 7 and 8 such thatlike reference numerals with the subscript "a" are applied to likecomponents thereof and most of the previous description is applicable.This embodiment of the forming apparatus 120a has its vacuum mold 122alocated at the upper position and its peripheral mold 126a is located atthe lower position. However, the downwardly facing surface 124a of theupper mold 122a has a convex shape and the lower peripheral mold 126ahas an upwardly concave shape. Furthermore, the mold surface 124a hasits vacuum openings 136a distributed over its entire extent. This vacuummold surface 124a may have straight line elements, curvatures intransverse directions, or inversely curved portions like the differentembodiments illustrated in FIGS. 11a, 11b, and 11c. Forming with theapparatus 120a proceeds as previously described in connection with FIGS.7 through 12 excepted for the reversed relationship of the upper andlower mold shapes.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

What is claimed is:
 1. A method for forming a heated glass sheetcomprising:sealing the periphery of the glass sheet against a fullsurface of a vacuum mold; initially communicating the vacuum moldsurface within the sealed periphery of the glass sheet with a vacuumreservoir to provide a vacuum impulse of at least 0.1 atmospheres ofvacuum to elastically form the glass sheet to the shape of the vacuummold surface; and thereafter terminating the vacuum impulse at apredetermined time so as to reduce optical distortion of the hot glasssheet as a result of engagement with the mold surface.
 2. A method as inclaim 1 wherein the vacuum impulse is provided at the vacuum moldsurface initially at a first level of vacuum and thereafter at a secondgreater level of vacuum.
 3. A method as in claim 2 wherein the first andsecond levels of vacuum are provided by communicating the vacuum moldsurface with a pair of vacuum reservoirs.
 4. A method as in claim 1, 2or 3 wherein the glass sheet periphery is sealed against the vacuum moldsurface by a pressing operation of a peripheral mold which maintains thepressed relationship as the vacuum impulse is provided at the vacuummold surface to form the glass sheet.
 5. A method as in claim 1, 2 or 3wherein the glass sheet periphery is initially sealed against the vacuummold surface by a pressing operation of a peripheral mold which isthereafter positioned out of engagement with the glass sheet as thevacuum impulse is provided at the vacuum mold surface to form the glasssheet.
 6. A method for forming a heated glass sheet comprising:sealingthe periphery of the glass sheet by a peripheral mold against a fullsurface of a vacuum mold; initially communicating the vacuum moldsurface within the sealed periphery of the glass sheet with a vacuumreservoir to provide a vacuum impulse of about 0.1 to 0.3 atmospheres ofvacuum to initially form the glass sheet to the shape of the vacuum moldsurface; thereafter communicating the vacuum mold surface with a vacuumreservoir to provide a second greater vacuum impulse of about 0.25 to0.7 atmospheres of vacuum to elastically form the glass sheet to theshape of the vacuum mold surface; and finally terminating the secondvacuum impulse at a predetermined time so as to reduce opticaldistortion of the hot glass sheet as a result of engagement with themold surface.
 7. A method for forming a heated glass sheetcomprising:sealing the periphery of the glass sheet by a peripheral moldagainst a full surface of a vacuum mold; initially communicating thevacuum mold surface within the sealed periphery of the glass sheet witha first vacuum reservoir to provide a vacuum impulse of about 0.1 to 0.3atmospheres of vacuum for about 0.5 to 2.0 seconds to initially form theglass sheet to the shape of the vacuum mold surface; thereaftercommunicating the vacuum mold surface within the sealed periphery of theglass sheet with a second vacuum reservoir to provide a second greatervacuum impulse of about 0.25 to 0.7 atmospheres of vacuum for about 0.5to 6 seconds to elastically form the glass sheet to the shape of thevacuum mold surface; and finally terminating the second vacuum impulseat a predetermined time so as to reduce optical distortion of the hotglass sheet as a result of engagement with the mold surface.